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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sat 17, 2016 7:40 am 
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john8750 wrote:
Flipperhome wrote:
The 12X4 is 3 bucks from ABCvacuumtubes. Can't get selenium rectifiers anymore, use modern diodes. Frankly, I'd use diodes for the 12X4 as well since I wouldn't go to the effort, and expense, of finding a "PAS3" transformer. Btw, you can find repro kits (which ain't cheap) for the PAS3 but they all invariably use a solid state power supply. See the various options here http://www.tubenirvana.net/pas3-main-page.html

That's not a divider on the tube heaters. They're DC, to cut hum, and that's just the ground reference.

The "weird pots" are almost unobtanium nowadays but modern amps don't do 'loudness' compensation anymore so just ignore that part of the schematic.

Btw, my 6BR8/6HB6 "Princely Pauper" is essentially a 'dollar days' version of the Dynaco ST-35 power section, although it's not exact. I didn't chose to employ the screen feedback but it could be implemented.

Thanks for the info Flip. I don't mind diodes either. Just wanted the music to see nothing but tubes. Do you believe having ultra linear screens would make a big difference?
Audio amps essentially have constant power draw (remember, 'peak' power is for transients) so the difference between vacuum and solid state diodes is non-existent under those conditions. The power is DC, who care where it comes from? Btw, the Dynaco ST-35 used solid state diodes in it's power supply.

UL taps might improve things but it comes at a cost, power output. The ST-35 makes up for that by over-volting the tubes to 370V. That might not sound like much but power increases as the square of voltage, and so does screen and plate dissipation, so it stresses the tubes. I felt that with the 6HB6 a more conservative approach was in order but you could certainly use UL taps on it at the correspondingly lower power output.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 1:57 am 
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I see Flip. So it would be good to use a constant current source when using an ultra linear circuit?

Check out this simple circuit. Very interesting.


http://www.electronixandmore.com/adam/i ... ematic.gif

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 3:17 am 
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john8750 wrote:
I see Flip. So it would be good to use a constant current source when using an ultra linear circuit?
Uh, no. That would be a very bad idea and, in any event, you're mixing apples with oranges. My fault for not being clear but I was speaking, in general, of the power supply. Some people feel that 'sag' produced by the vacuum tube rectifier when delivering 'full current' (i.e. a max power) somehow contributes to the 'sound', but it doesn't because that 'power' only occurs during transient peaks and is delivered by the filter caps. It's a different story with guitar amps where they really are used at 'max power' (but even then I'm not convinced droop is 'desirable').

At any rate, for audio amps average power is within the 'Class A' portion of the AB and, so, there is no 'sag' or, indeed, any appreciable change to the power supply average current draw. In fact, any 'change' or ripple on the B+ rail is a potential 'problem' as it can lead to feedback (through the power supply) and one example is motor boating (low frequency oscillation). Ideally, B+ voltage should be rock solid and a perfect sink to any signal (i.e. a constant voltage, not current), just as the ground rail is, and the only reason a simple RC filter comes even close is because the (average) current draw is essentially constant (with transient surges handled by the caps). Note that I keep saying AVERAGE current because instantaneous varies at any given moment in time but AVERAGES to a constant value. A power supply that's a constant current source would prevent that variation, necessary for 'audio', as well as the transient peaks. Or rather, would introduce massive feedback and distortion as it varied voltage trying to keep current constant. Hard to say exactly what it would do because it would depend on the amp's design but needless to say it would no longer be an 'audio' amp.

Constant current sources can be used on individual stages but, in those cases, are not part of the power supply but the stage itself (and a different discussion).

All of that is true whether one uses UL taps or not.

john8750 wrote:
Check out this simple circuit. Very interesting.


http://www.electronixandmore.com/adam/i ... ematic.gif
Cute circuit but certainly not Hi-Fi in either power output or distortion.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 5:40 am 
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Flipperhome wrote:
john8750 wrote:
I see Flip. So it would be good to use a constant current source when using an ultra linear circuit?
Uh, no. That would be a very bad idea and, in any event, you're mixing apples with oranges. My fault for not being clear but I was speaking, in general, of the power supply. Some people feel that 'sag' produced by the vacuum tube rectifier when delivering 'full current' (i.e. a max power) somehow contributes to the 'sound', but it doesn't because that 'power' only occurs during transient peaks and is delivered by the filter caps. It's a different story with guitar amps where they really are used at 'max power' (but even then I'm not convinced droop is 'desirable').

At any rate, for audio amps average power is within the 'Class A' portion of the AB and, so, there is no 'sag' or, indeed, any appreciable change to the power supply average current draw. In fact, any 'change' or ripple on the B+ rail is a potential 'problem' as it can lead to feedback (through the power supply) and one example is motor boating (low frequency oscillation). Ideally, B+ voltage should be rock solid and a perfect sink to any signal (i.e. a constant voltage, not current), just as the ground rail is, and the only reason a simple RC filter comes even close is because the (average) current draw is essentially constant (with transient surges handled by the caps). Note that I keep saying AVERAGE current because instantaneous varies at any given moment in time but AVERAGES to a constant value. A power supply that's a constant current source would prevent that variation, necessary for 'audio', as well as the transient peaks. Or rather, would introduce massive feedback and distortion as it varied voltage trying to keep current constant. Hard to say exactly what it would do because it would depend on the amp's design but needless to say it would no longer be an 'audio' amp.

Constant current sources can be used on individual stages but, in those cases, are not part of the power supply but the stage itself (and a different discussion).

All of that is true whether one uses UL taps or not.

john8750 wrote:
Check out this simple circuit. Very interesting.


http://www.electronixandmore.com/adam/i ... ematic.gif
Cute circuit but certainly not Hi-Fi in either power output or distortion.



I thought it was an excellent circuit to show the very basics of an amp. And the basic tube valve.
BTW- where can I get the tubes for your Pauper amp?
The power transformer you show for that amp has a single primary of 220 volts. What other can you suggest?
I have no problem using a couple diodes for the B+. So don't need the 5 volt winding.
I need to order asap. Along with the OT's. Cant start the amp for awhile though. Thanks again.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 5:43 am 
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OOPS- The Pauper does not have a rectifier tube anyway.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 6:06 am 
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john8750 wrote:
I see Flip. So it would be good to use a constant current source when using an ultra linear circuit?

Check out this simple circuit. Very interesting.


http://www.electronixandmore.com/adam/i ... ematic.gif

JOHN:
did you mean a "constant current" power supply for B+
or were you referring to the CCS as a form of output-tube bias just like we are using for the 5902/and/6v6gt amp?

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 6:40 am 
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john8750 wrote:
I thought it was an excellent circuit to show the very basics of an amp. And the basic tube valve.
BTW- where can I get the tubes for your Pauper amp?
The power transformer you show for that amp has a single primary of 220 volts. What other can you suggest?
I have no problem using a couple diodes for the B+. So don't need the 5 volt winding.
I need to order asap. Along with the OT's. Cant start the amp for awhile though. Thanks again.
Rats. I didn't notice there wasn't a 120VAC option. Well, the next one up is the XPWR065. Same heater power, no rectifier, and 250 mA @ 500VCT. That's 'more than enough' so B+ may rise a bit.

Be aware that you may need to tweak things a little so build it in stages so you can debug each one. Power supply first, then the outputs and make sure idle current is correct, then the preamp. Once one channel is right the second should go without a hitch.

Tubes can be had from abcvacuumtubes.com. That's where I go to check prices and they're both dollars days right now.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 8:15 am 
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john8750 wrote:
I thought it was an excellent circuit to show the very basics of an amp. And the basic tube valve....
It is that and in the early days that was a common design, albeit with triode outputs.

The 1995 Popular Electronics article (page 53 in http://www.americanradiohistory.com/Arc ... 995-01.pdf ) says it does 3 Watt but I'm not sure I believe that because of OPT impedance. At 8k PP that's 4k per side (when operating Class A) and that's 33% more than the Class A single ended load which produces 1.3 Watt... and at 110V plate, instead of 92V, to boot. I think you'd be lucky to get 2 Watt out of it.

It made sense in 1920, when tubes were expensive and iron was cheap, but with the OPT alone running 80 bucks each that's an awfully expensive toy for only 2 Watt of output and if I'm going to spend that much on iron it only seems prudent to put a little more effort into the 'tube' portion for a 10 or 15 Watt amp.


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 7:55 pm 
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Pbpix wrote:
john8750 wrote:
I see Flip. So it would be good to use a constant current source when using an ultra linear circuit?

Check out this simple circuit. Very interesting.


http://www.electronixandmore.com/adam/i ... ematic.gif

JOHN:
did you mean a "constant current" power supply for B+
or were you referring to the CCS as a form of output-tube bias just like we are using for the 5902/and/6v6gt amp?




I was wondering about tube cathode constant current. Yes, as we did on the 5902 and 6V6 amps.
What do you think about it Professor? Something sure made those amps sound superior.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 8:10 pm 
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OK men
The XPWRO65 is $61.98 and the GPXPP10-8's are $28.73 each. The speaker taps will be 8ohms. I want to order them right away, and also the tubes.
Let me know of any other thoughts that have to do with this. I'm getting excited again. Like goose bumps. Thank you men. I'm a cheap date.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 8:14 pm 
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Flipperhome wrote:
john8750 wrote:
I thought it was an excellent circuit to show the very basics of an amp. And the basic tube valve....
It is that and in the early days that was a common design, albeit with triode outputs.

The 1995 Popular Electronics article (page 53 in http://www.americanradiohistory.com/Arc ... 995-01.pdf ) says it does 3 Watt but I'm not sure I believe that because of OPT impedance. At 8k PP that's 4k per side (when operating Class A) and that's 33% more than the Class A single ended load which produces 1.3 Watt... and at 110V plate, instead of 92V, to boot. I think you'd be lucky to get 2 Watt out of it.

It made sense in 1920, when tubes were expensive and iron was cheap, but with the OPT alone running 80 bucks each that's an awfully expensive toy for only 2 Watt of output and if I'm going to spend that much on iron it only seems prudent to put a little more effort into the 'tube' portion for a 10 or 15 Watt amp.



I guess it wouldn't make much difference to an un-audiophile. I do agree.
Think I will stay with the Pauper this time.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 8:18 pm 
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Flipperhome wrote:
john8750 wrote:
I thought it was an excellent circuit to show the very basics of an amp. And the basic tube valve.
BTW- where can I get the tubes for your Pauper amp?
The power transformer you show for that amp has a single primary of 220 volts. What other can you suggest?
I have no problem using a couple diodes for the B+. So don't need the 5 volt winding.
I need to order asap. Along with the OT's. Cant start the amp for awhile though. Thanks again.
Rats. I didn't notice there wasn't a 120VAC option. Well, the next one up is the XPWR065. Same heater power, no rectifier, and 250 mA @ 500VCT. That's 'more than enough' so B+ may rise a bit.

Be aware that you may need to tweak things a little so build it in stages so you can debug each one. Power supply first, then the outputs and make sure idle current is correct, then the preamp. Once one channel is right the second should go without a hitch.

Tubes can be had from abcvacuumtubes.com. That's where I go to check prices and they're both dollars days right now.



Thanks Flip, and will proceed slowly.
I was hoping Peter would B-Board it for something to do.
Maybe add some CCS technology.
Might start a new thread for this amp.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 9:40 pm 
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john8750 wrote:
Pbpix wrote:
john8750 wrote:
I see Flip. So it would be good to use a constant current source when using an ultra linear circuit?

Check out this simple circuit. Very interesting.


http://www.electronixandmore.com/adam/i ... ematic.gif

JOHN:
did you mean a "constant current" power supply for B+
or were you referring to the CCS as a form of output-tube bias just like we are using for the 5902/and/6v6gt amp?

I was wondering about tube cathode constant current. Yes, as we did on the 5902 and 6V6 amps.
What do you think about it Professor? Something sure made those amps sound superior.

Yes John you can use an LM317 for CCS to replace almost any cathode-bias (aka self-bias) resistor.

It provides a nice solid fixed current through the cathodes by varying the resistance/voltage as needed for idle bias. This idea totally eliminates any need of trying to find matched tubes ( for PP) because the CCSs will make both tubes operate exactly identically at zero signal idle.
Additionally, by-passing the CCSs with a good sized capacitor provides a low impedance dynamic current source as the dynamic signal is applied to the grid.

Additionally, coupling the cathodes together with back to back e-caps provides PSRR (Power Supply Rejection Ratio)
[It works so as to to cancel any hum from the power supply]
(https://en.wikipedia.org/wiki/Power_sup ... tion_ratio)

The application of by-passed CCS in a PP amp creates a cross between fixed bias and self bias.

As we have both experienced (to our great pleasure)... it truly sounds and operates beautifully.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 11:14 pm 
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Great Peter, I will make the change. I will finish my other work first. Should take a few weeks to get the transformers. How can I tell what type Edcor
transformers I have? Are they marked? I have a pair on the second 6V6 that I don't need, but cant remember what they are.
Are you busy in the shop right now? I need to hire you. :lol:

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Sun 18, 2016 11:44 pm 
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john8750 wrote:
Great Peter, I will make the change. I will finish my other work first. Should take a few weeks to get the transformers. How can I tell what type Edcor
transformers I have? Are they marked? I have a pair on the second 6V6 that I don't need, but cant remember what they are.
Are you busy in the shop right now? I need to hire you. :lol:

I think those were the ones you bought for building a 5902 amp for your cousin?

If so.. i think they are probably 16 ohm to 8k ( can be used as 8-ohm to 4k)
The 5902 requires 4k primary

So if you use 8 ohm speakers on the 16 ohm secondary you'll reflect 4k back to the tube.

Xpp-10 watt
8k - 16ohm

http://edcorusa.com/xpp10-8k

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Mon 19, 2016 12:11 am 
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Peter, the OT's I need are going to be the GPXPP10-8K. Seems like the ones I have are something like this, but don't know how to tell.
No markings on the can. Is there a way to tell by reading winding resistance?
I will go ahead and order a new set. Cheap enough.
So, have you looked at Flip's Pauper circuit? Should I order two sets of tubes?

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Mon 19, 2016 12:17 am 
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Change order
Is this the correct OT for the Pauper?
http://www.edcorusa.com/cxpp10-8k
I might as well get the best. Very affordable and bigger is better.

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Mon 19, 2016 1:09 am 
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john8750 wrote:
Change order
Is this the correct OT for the Pauper?
http://www.edcorusa.com/cxpp10-8k
I might as well get the best. Very affordable and bigger is better.

On his schematic it shows an XPP10 8-8k

I don't know what the resistors are between the plate and the OT?

Image

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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Mon 19, 2016 1:33 am 
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Pbpix wrote:
john8750 wrote:
Change order
Is this the correct OT for the Pauper?
http://www.edcorusa.com/cxpp10-8k
I might as well get the best. Very affordable and bigger is better.

On his schematic it shows an XPP10 8-8k

I don't know what the resistors are between the plate and the OT?

Image
It can take any of the XPP, CXPP, or GXPP as long as they're 8K plate to plate but as the title suggests, 'Pauper," I listed the XPP since it's the least expensive. The original idea was the SPECO T7010 but they changed it to something no longer suitable.

The unmarked 'resistors' simulate internal OPT winding resistance for SPICE and aren't a part of the schematic (which is why they aren't marked).


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 Post subject: Re: 6V6 / 6AQ5 PP Stereo Amp
PostPosted: Sep Mon 19, 2016 1:57 am 
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john8750 wrote:
Change order
Is this the correct OT for the Pauper?
http://www.edcorusa.com/cxpp10-8k
I might as well get the best. Very affordable and bigger is better.
Yes, that's the one.

Since everyone seems to be 'picky' :wink: I'll point out that's a 10 Watt OPT and the amp does 15 watt (and maybe a little more) so if you want 'bigger is better' you could move up to the CXPP25-8k (/23 if you want to play with UL taps).

I don't think it's necessary (obviously since I spec'd 10 Watt) since an OPT will pass much more power at the higher frequencies than the low and that 'extra' 5 Watt over 10 Watt would be nothing but transient peaks.

Btw, being cathode bias the amp won't do 15 Watt continuous (cathode voltage rise) so it's more a case of specmanship whether you use 10 Watt or 25 Watt (which is the nearest to 15 Watt in the CXPP). Now, they do have a 15 Watt in the GXPP but that's the 40 Hz job.


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